Perito Moreno Glacier

While roughly ninety percent of the world's glaciers are shrinking, Perito Moreno spent most of the twentieth century doing something almost nobody's glacier does: holding its ground, even pushing forward by a couple of meters some days, fed by heavy Andean snowfall high on the Southern Patagonian Ice Field and kept in balance by constant, thunderous calving into the lake below.

That advance creates one of the strangest natural cycles anywhere. As the glacier's front pushes across a narrow point in Lago Argentino, it welds itself to the rock on the far shore and dams the Brazo Rico arm of the lake completely. With nowhere to drain, the water trapped behind the ice can rise as much as 30 meters above the level of the main lake — until the pressure finally wins, tunneling under or through the ice and triggering a rupture that empties the swollen arm in a spectacular rush of water and collapsing ice. It has happened as often as once a year and as rarely as once a decade; there's no fixed schedule, which is part of why people wait for it.

The equilibrium is showing cracks, though. Recent measurements show the ice surface dropping and the glacier's flow speeding up even as its front position wavers, and researchers now think Perito Moreno may be approaching the point where it stops reaching the opposite shore for good — ending a rupture cycle that has run, on and off, for as long as anyone has kept records.

Good to know

It's recognised as an IUGS Geological Heritage Site, one of a short list of sites worldwide flagged for their scientific value in understanding how glaciers actually behave.

Best time to visit

Southern hemisphere summer (December–February) is warmest and busiest; the shoulder months of March–April and October–November bring thinner crowds while boat trips out to the ice face still run reliably.

Getting there

63 km from El Calafate. El Calafate - Commander Armando Tola International Airport (FTE) is about 80 km away.